DESCRIPTION: The diagnostic and therapeutic modalities available to emergency physicians treating patients with possible myocardial ischemia (MI) are rapidly expanding. Although these therapies offer the potential to decrease morbidity and mortality, their use may also increase costs and expose patients to treatment-related effects. To minimize costs and avoid unnecessary risk of therapy-related complications, treatments must be targeted only to those most likely to gain a benefit. To accomplish this, physicians must be able to rapidly diagnose and risk stratify patients. Increasingly, measurement of laboratory markers of myocardial injury such as myoglobin, CK-MB, and troponins are being utilized for this purpose. Further, a new generation of laboratory assays is being rapidly developed. Rather than detecting cell death, these "markers of coronary thrombosis" will allow direct assessment of the thrombotic state of the patient's coronary arteries at presentation. In the near future, emergency physicians are likely to utilize the new assays along with traditional data sources when making treatment and disposition decisions. No scientifically derived framework exists to aid the physician in interpreting these tests. In addition, the value of these assays for diagnosis or risk stratification has not been systematically studied or directly compared, and no cost-effectiveness studies have been conducted. A predictive instrument able to accurately estimate a patient's probability of MI, as well as the subsequent risk of complications and the need for emergent interventions, would significantly improve the physician s ability to make optimal treatment and disposition decisions. In the proposed study, clinical data and sera from 3,200 patients with possible ischemia presenting to three emergency departments (ED) will be collected, and serum levels of various markers will be measured. The predictive values of the markers, both alone and in combination, will then be determined. Further, by applying statistical techniques to the prospectively collected clinical and laboratory data, a predictive instrument capable of risk stratification of ED patients with possible ischemia will be derived. The ED physician's judgement will then be compared to the potential clinical utility and cost effectiveness of this "comprehensive predictive instrument" for both diagnosis and risk stratification.